potassium-40

Definitions

from Wiktionary, Creative Commons Attribution/Share-Alike License

n. A naturally-occurring radioactive isotope of potassium, 4019K, having nineteen protons and twenty-one neutrons, and a half-life of 1.3 billion years; it is the chief source of natural radioactivity in living tissue

Etymologies

Sorry, no etymologies found.

Examples

(Presumably, the need for a license is a matter of degree, given that our own bodies contain radioactive potassium-40, and given that the walls of most buildings contain the radioactive isotopes from the natural uranium-238 and thorium-232 decay chains).

Presumably the individual particles of silt or sand that go to make sedimentary rocks contain potassium-40 and other radioactive isotopes, and therefore could be said to contain radioactive clocks; but unfortunately these clocks are no use to us because they are not properly zeroed, or are zeroed at different times from each other.